Great question. I sometimes find that the designers of a product can be so invested in the existing design approach, that they risk being biased (or less neutral) when facilitating the test. So, whenever possible, I suggest that the designers observe the tests while someone else facilitates. The person facilitating may be a usability professional on the team or another team member familiar with the usability testing process.

Having said that, as a designer, if your only option is to facilitate your own tests, I would go ahead and do so. In my experience, any testing is better than no testing at all. I expect, as you start facilitating the tests, you’ll be surprised by how much you can learn from observing the users. While it’s more of a challenge to facilitate the tests as a designer, you can still gather a ton of invaluable data.

Christine